Method and Device for Heating, In Particular Highly Viscous Products

ABSTRACT

A method for heating, in particular of highly viscous products, and a device for performing the method, wherein the product is pre-heated to a first temperature T1 in a first step with at least one product/water heat exchanger section with water as the heating medium, wherein the water cools down. The product is further heated to a second temperature T2 in a second step with at least one product/product heat exchanger section  2   a  with the product as a heating medium, wherein the returning product serving as heating medium is cooled down, and is then further heated to a third temperature T3 in a third step with at least one product/water heat exchanger section  3   a  with water as the heating medium, wherein the water cools down and wherein the heated product is then recirculated as heating medium for heating the product.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority of German Application No. 102009036019.0, filed Aug. 4, 2009. The entire text of the priority application is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure relates to a method for heating, in particular highly viscous products, as well as to a device for performing this method.

BACKGROUND

At present, there are basically two different processes for thermal, aseptic heating by means of heat exchangers.

On the one hand, there is the product-against-product process. In this process, heat exchangers are used in which the incoming product is heated by a product that has been heated to a higher temperature beforehand. In particular, plate heat exchangers, but if the design of the secondary side is correspondingly hygienic, also tubular heat exchangers are suited for this. Such a process permits high heat recovery of 90 to 95% and permits to reduce the heat exchanger area that is required for heating. Thus, investment costs and the area required can be reduced. This technique is disadvantageous in that this process is economically suited only for low-viscous products (up to a maximum of 5-15 mPas) in common heat exchangers with smooth heat exchanger areas. Meanwhile, heat exchangers that comprise an uneven, structured surface to improve heat transfer are also available. In these heat exchangers, viscosity can be somewhat higher, but here, too, there are limits to viscosity (up to a maximum of 25 mPas), so that products, such as syrups and smoothies, can neither be economically heated. It showed that the poor heat transfer on both sides due to high viscosity requires a larger heat exchanger area, compared to a product against water application, and thus economically reaches its limit of application.

Therefore, a product against water process is used in particular for highly viscous products. This process is suited for all products, even for those having high viscosity, that means products with viscosities >15 mPas. It has high flexibility with respect to the temperature and product ranges (i.e. products of different viscosities that are passed through a system). However, a disadvantage of this process is the lower heat recovery (80 to 87%). Here, higher investment costs result due to larger required heat exchanger areas and thus heat exchanger modules to be installed.

SUMMARY OF THE DISCLOSURE

Starting from this situation, an aspect underlying the present disclosure is to provide a method as well as a device for heating products which are also suited for heating highly viscous products and permit high heat recovery at low investment costs.

The method according to the disclosure as well as the device according to the disclosure permit a product/product heat exchanger process also for highly viscous products, where high heat recovery rates at low investment costs and with compact systems are possible. That means, according to the present disclosure, in a first step, the product is pre-heated to a first temperature T1 with at least one product/water heat exchanger section with water as a recuperative heating medium, where the water cools down. Only then, the pre-heated product is, in a second step, further heated to a second temperature T2 in a product/product heat exchanger section. By pre-heating the product in the first step, the viscosity of the product is reduced, so that a better heat transfer in the product/product heat exchanger section—i.e. in the second step—results. In the third step, high-temperature heating to the desired product treatment temperature can then be performed with heating water. The product heated in the third step can then be recirculated and used as heating medium for heating the product in step two. Compared to the classic water swing, this method or this device, respectively, permits a smaller system periphery, a lower number of pumps and equalizer heat exchangers. Less heat exchanger sections or modules are required than in the classic water swing with a better heat recovery (90 to 95%). The efficiency is only slightly lower than in the classic product/product applications. The method according to the disclosure or the device according to the disclosure, respectively, permit higher flexibility with respect to the variation of the inlet temperatures and the directly resulting outlet temperatures, as with the preceding product/water section on the secondary side, heat transfer can be adjusted with respect to temperature and flow. The degassing or the homogenization temperature is independent of the constricted product/product process in the first section, as with the preceding product/water section, heat transfer can be adjusted on the secondary side with respect to temperature and flow. The low-temperature sections are not recuperatively operated with the product as cooling medium.

According to a preferred embodiment of the present disclosure, the product that has been cooled down in step two is cooled down to a temperature T5 in a fourth step with at least one product/water heat exchanger section 4 a, wherein water that has been cooled down in the first step is used as cooling medium.

Thus, the heating medium of step 1 which cools down in step 1 can be advantageously used for cooling the returning product, which clearly improves the efficiency of the method or the device, respectively. It is advantageous for the heated water of the fourth step to be recirculated and used in step 1 as heating medium for pre-heating the product, where then the water cooled down in step 1 can be used again as cooling medium in step 4. The water cycle between the product to be heated and the return product to be cooled in turn improves heat recovery.

Advantageously, the product is heated to a temperature T1 in step 1, so that the viscosity of the product is then lower than 15 mPa s, preferably lower than 5 mPa s. If specially structured internal tubes are employed for generating increased turbulences in tubular heat exchangers, the viscosity range can be shifted upwards. That means that for this case of application viscosity is then to be lower than 25 mPa s, preferably lower than 10 mPa s at the outlet of the first heat exchanger region. If a plate heat exchanger is employed, the viscosity range can be shifted still further upwards. Thus, good heat transfer can be ensured. That means that in the heating region in step 1, the product must be heated to such a high temperature that the outlet viscosity as indicator falls below a critical value. The exact temperature and viscosity values, however, depend on the respective product. Apart from the viscosity, density is reduced as temperature rises, and thermal capacity and thermal conductivity increase as temperature rises, which also makes the heat transfer and effectiveness of a product/product application rise.

According to the disclosure, T1<T2<T3, i.e. the temperature of the product, is increased in the heating regions, where the temperature T3 then corresponds to the desired product treatment temperature, which is, for example, required for the thermal treatment of the product to ensure its microbiological stability.

The disclosure permits the heating of products of which the original viscosity at 20° C. with a corresponding shearing rate (for example 300 to 800 l/s) is within a range of >5 mPa s, preferably within a range of 5 mPa s to 100 mPa s.

Advantageously, with a performance regulation, the product can be passed by the first heat exchanger region via a product bypass, i.e. by the at least one product/water heat exchanger section.

For performing steps 1, 2, 3, the device according to the disclosure for performing the method comprises a corresponding first, second and third heating region which each comprises at least one heat exchanger section. A heat exchanger section here comprises at least one heat exchanger, in particular at least one tubular heat exchanger or plate heat exchanger. If there are several heat exchanger sections in the heating region, these are connected in series on the product side. The heating regions or their heat exchanger sections are interconnected such that water as a heating medium can be supplied in the first heating region for pre-heating, and in the second heating region, returned product can be supplied that was heated with water in a third heating region.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be illustrated below in greater detail with reference to the following figures:

FIG. 1 schematically shows the structure of a device for performing the method according to the disclosure according to a preferred embodiment.

FIG. 2 roughly schematically shows a section through a tubular heat exchanger module.

FIG. 3 shows a diagram which indicates the course of viscosity, density, thermal capacity and thermal conductivity of a product in response to temperature.

FIG. 4 schematically shows several heat exchangers connected in series.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a device for heating a product, in particular for thermally heating a product. Such a device is in particular employed in the beverage industry for sterilizing beverages or other liquid food. However, the device is also suited for all recuperative applications, in particular for heating highly viscous products.

As can be taken from FIG. 1, the device comprises a product inlet 7 through which the product flows into the device. The course of the product to be heated is represented by the dot-dash line, the course of the water by the solid line, and the course of vapor by the dashed lines. The device comprises a first heating region 1 which comprises at least one product/water heat exchanger section 1 a by which the product can be pre-heated to a pre-heating temperature T1 with water as the heating medium. In FIG. 1, only one heat exchanger section 1 a is shown. However, several first product/heat exchanger sections 1 a can also be connected in series. FIG. 4 shows generally a series connection of heat exchanger sections, where the outlet of a first section a is connected to the inlet of a subsequent section b for heating or cooling a product. Equally, the outlet of a section c for a heating-cooling medium is connected to the inlet of a section b following in the flow direction of the medium.

The product/water heat exchanger section 1 a here comprises an inlet 8 for the product and an outlet 9 for the heated product. Furthermore, the heat exchanger section 1 a comprises an inlet 11 for heating medium (here: water) and an outlet 10 for the cooled heating medium. Via a corresponding conduit 12, the first heating region is connected to a second heating region 2. The second heating region 2 also comprises at least one product/product heat exchanger section 2 a by which the pre-heated product from the heating region 1 can be further heated to a temperature T2 with the heated returning product as the heating medium. Here, the product/product heat exchanger section 2 a comprises an inlet 13 for product to be heated, as well as an outlet 14 for the heated product. Furthermore, the heat exchanger section 2 a comprises an inlet 15 for a heating medium, here for returning product, and an outlet 16 for the cooled returning product. Preferably, the two flows are guided in all described sections in a reverse flow.

The outlet 14 of the heat exchanger section 2 a is connected to the inlet 18 of the product/water heat exchanger section 3 a of a third heating region 3 via a conduit 17, where the third heating region 3 comprises at least one product/water heat exchanger section 3 a. The product/water heat exchanger section 3 a further heats the product from the second heating region 2 to a temperature T3 with water as the heating medium. The heat exchanger section 3 a comprises an outlet 19 for heated returning product and furthermore an inlet 20 for the heating medium, here: water, or vapor, respectively, and an outlet 21 for the cooled heating medium.

From the outlet 19, the product heated to a product treatment temperature T3 is returned as heating medium back to the second heating region 2 via the conduit 22. In particular, the returning product enters the inlet 15 of the heat exchanger section 2 a and can thus heat the product that is supplied via the inlet 13. Thereby, the returning product, which is the heating medium for the third heating region 3, preferably cools down in a reverse flow.

Furthermore, a supply for vapor 25 is provided which supplies vapor to a hot water apparatus 27, so that then hot water is supplied to the third heating region 3, i.e. the heat exchanger section 3 a via the inlet 20. Via the conduit 23, the outlet 21 is connected to the inlet 20 via the hot water apparatus 27, so that the cycle 6 is formed. The condensate is discharged from the hot water apparatus 27 via the condensate conduit 26, while new vapor can be supplied via the conduit 25. The hot water is circulated by means of the pump 24.

The second heating region 2 is followed by a cooling region 4 which comprises at least one product/water heat exchanger section 4 a. Here, the heat exchanger section 4 a comprises an inlet 28 for returning product to be cooled and an outlet 29 for the cooled product. Furthermore, the section 4 a comprises an outlet 30 for the then heated water. The outlet 30 is connected to the inlet 11 of the heat exchanger section 1 a via the conduit 51. Thus, the water heated in the section 4 a can be supplied to the pre-heating region as heating medium. Then, the water cooled in section 1 can be again supplied to the inlet 31 via the outlet 10 of the section 1 a via the circulation conduit 32. The water can be circulated by means of the pump 33. The product/water heat exchanger section 4 a furthermore comprises an outlet 29 for returning cooled down product. Optionally, a further, non-recuperative intense cooler 41 is provided.

Finally, a bypass conduit 39 can be optionally provided which can bridge the first heating region 1 in a partial flow. For this, a corresponding control valve 40 is provided in the conduit 39.

As already mentioned, only one heat exchanger section is represented in FIG. 1 for the individual heating regions or the cooling region, respectively. However, these heating regions can contain an arbitrary number of sections which are then each connected in series on the product side and interconnected as unit as the sections shown in FIG. 1. That means that the respective intake is effected for several sections e.g. via the inlet of the first section and the outlet via the outlet of the last sections arranged in series.

One heat exchanger section here comprises at least one heat exchanger module. In FIG. 2, one example of a tubular heat exchanger module is shown which is employed, for example, in the embodiment shown in FIG. 1 and which comprises tubes with smooth heat transfer surfaces. Smooth surfaces are advantageous for hygienic reasons. The module shows an inlet 36 on the secondary side and an outlet 37 on the secondary side, which are arranged in this embodiment in the shell 38 or external tube of the heat exchanger. Furthermore, the tubular heat exchanger comprises several banks of tubes with a corresponding inlet 34 and outlet 35 on the primary side. Primary side means the flow through the internal tubes 55 of the module. Advantageously, in a product/water tubular heat exchanger, the product which is to be heated flows in the tubes 55, that means primarily. In a product/product heat exchanger, the product to be heated which is not yet sterile, flows outside the tubes 55, that means secondarily, and the sterile heated product flows primarily, i.e. in the tubes 55. This is because internal tubes offer higher hygienic safety.

If several heat exchanger modules are arranged in one section, these are arranged in series, i.e. the outlet 35 of a first module is connected to the inlet 34 of a subsequent module, and the outlet 37 is connected to the inlet 36 of a subsequent module.

Below, the method according to the disclosure will be illustrated more in detail with reference to FIG. 1. The method according to the disclosure is in particular suited for highly viscous products with a viscosity >5-100 mPas. As is in particular represented in FIG. 3, the viscosity of a product depends on the product temperature. FIG. 3 shows a product which has a high initial viscosity, e.g. of 20 mPas, at a temperature of 20° C. As can be taken from FIG. 3, viscosity is so high at temperatures of <60° C. that a product/product heat exchanger process is not economical due to the poor heat transfer. Only in a range of >about 60° C., viscosity is reduced to such an extent that a product/product heat exchanger process is also economically possible. At the same time, density is also reduced as temperature rises, and thermal capacity and thermal conductivity rise. For this reason, the product which enters the device, for example, at a temperature of 5 to 35° C., here e.g. 15° C., is, in a first step, cooled down to a first temperature T1 with water as the heating medium with at least one product/water heat exchanger section 1 a, while the heating medium is cooled down. In the process, the product is heated in step 1 to such a high temperature that the outlet viscosity as indicator, but also the density, thermal conductivity and thermal capacity fall below a critical value. That means that with smooth tube surfaces the viscosity at the outlet 9 is to be lower than 15 mPa s, preferably lower than 5 mPa s. If specially structured internal tubes are employed in tubular heat exchangers, the viscosity range can be clearly shifted upwards. That means that for this case of application, viscosity is then to be lower than 25 mPa s, preferably lower than 10 mPa s at the outlet 9. If a plate heat exchanger is employed, the viscosity range can be shifted still further upwards. The temperature T1 to which the product is heated, is, for example, within a range of between 30° C. and 80° C., preferably 50° C. to 70° C., depending on the initial viscosity of the product. Here, the product is supplied on the primary side and the heating medium water on the secondary side.

The pre-heated product which is now no longer highly viscous can now be further heated to a second temperature T2 in a second step with at least one product/product heat exchanger section 2 a with returning product as the heating medium, where the returning product serving as heating medium is cooled down. The product can thus be heated to a temperature T2, for example within a range of 72° C. to 135° C.

In the product/product heat exchanger section 3 a, the product to be heated is supplied on the secondary side, and the returning cooling product on the primary side. In a third step, the product is then further heated to a third temperature T3 with at least one product/water heat exchanger section 3 a with water as the heating medium, where the water preferably cools down in a reverse flow. The product can here be heated to a high temperature, i.e. to the desired product treatment temperature, e.g. for sterilization. The temperature can be, for example, within a range of 90° C. to 140° C. The heating medium, i.e. here the water, is guided in a cycle 6, where vapor is supplied to the hot water apparatus via a conduit 25 and condensate is discharged via a conduit 26.

The highly heated product is then returned to the second heating region 2 via the conduit 22 and here serves as heating medium, while it is simultaneously cooled down to a temperature T4 which is lower than the temperature T3. The temperature T4 can be, for example, within a range of 55° C. to 65° C.

For further cooling the returning product, the product is cooled to a temperature T5 in the cooling region 4 via the at least one product/water heat exchanger section 4 a. The temperature T5 is, for example, within a range of between 17° C. and 25° C. The product to be cooled is supplied on the primary side, the cooling medium, here the water, is supplied on the secondary side. The cooled returning product can be optionally supplied to a further cooler 41, to a buffer tank or directly to a filling device. The cooling medium which is used for the cooling region 4 is the water that has been cooled down in the first step, i.e. in the first heating region 1.

When it is entering the cooling region, the cooling medium has, for example, a temperature of 10° C. to 15° C., here depending on the product inlet temperature. The water that is guided through the cooling region is pumped to the pre-heating region 1 in a cycle and again serves as heating medium for pre-heating the product. This heating medium has, for example, a temperature within a range of 55° C. to 75° C. when it is entering the first heating region 1. Thus, the cooling medium of the cooling region 4 can be effectively used for pre-heating the product, so that the viscosity of the product can be reduced.

In case of a performance regulation of the product for initially cooling it, it can be advantageous not to guide the product through the heating region 1, but to pass a partial flow by the first heating region 1 via the product bypass 39 with a controlled valve 40 and to admix it to the product downstream of the outlet 9 in a cold state, where the flow ratio between the bypass conduit 39 and the heating region 1 can be adjusted by the control valve 40.

In the previous embodiment, water was indicated as the heating medium. In the cycle 5 and 6, water is in its liquid phase. In the cycle 6, energy is continuously supplied to the circulation water with vapor via the hot water apparatus 27, which passes into the product during the heating in stage 3.

That means that the present disclosure permits a product/product heat exchanger process also for highly viscous products, such as for example fruit juices, syrups, smoothies. 

1. Method for heating, in particular of highly viscous products, comprising: pre-heating the product to a first temperature (T1) in a first step with at least one product/water heat exchanger section with water as the heating medium, wherein the water cools down, further heating the product to a second temperature (T2) in a second step with at least one product/product heat exchanger section with the product as a heating medium, wherein the product serving as heating medium is cooled down, and further heating the product to a third temperature (T3) in a third step with at least one product/water heat exchanger section with water as the heating medium, wherein the water cools down and wherein the heated product is then recirculated as heating medium for heating the product in the second step.
 2. Method according to claim 1, wherein, after the recirculated product has been cooled down in the second step, cooling down the product to a temperature (T5) in a fourth step with at least one product/water heat exchanger section, where water that has been cooled down in the first step is used as cooling medium.
 3. Method according to claim 2, and circulating the heated water of the fourth step which heated water serves as heating medium for pre-heating the product in the first step, and the water cooled down in the first step serves as cooling medium in step four.
 4. Method according to claim 1, wherein the product is heated to a temperature in step 1, such that the viscosity of the product is lower than 25 mPa·s with structured heat exchanger areas and lower than 15 mPa·s with smooth heat exchanger areas.
 5. Method according to claim 1, wherein T1<T2<T3.
 6. Method according to claim 1, wherein the initial viscosity of the product to be heated at 20° C. is within a range of >5 mPa·s.
 7. Method at least according to claim 1, wherein for performance regulation, passing the product by the at least one product/water heat exchanger section in a partial flow via a product bypass.
 8. Device for performing the method according to claim 1, comprising: a product inlet, a first heating region which comprises at least one product/water heat exchanger section by which the product can be pre-heated to a pre-heating temperature (T1) with water as the heating medium, a second heating region comprising at least one product/product heat exchanger section by which pre-heated product from the heating region can be further heated to a temperature (T2) with the product as the heating medium, and a third heating region comprising at least one product/water heat exchanger section by which the heated product from the second heating region can be further heated to a temperature (T3) with water as the heating medium, wherein the heated product from the third heating region is recirculated to the second heating region as heating medium.
 9. Device according to claim 8, wherein a heat exchanger section comprises at least one heat exchanger.
 10. Device according to claim 8 wherein the heat exchanger sections of a respective heating region are connected in series.
 11. Device according to claim 8, wherein the device further comprises: a cooling region which comprises at least one product/water heat exchanger section by which the product cooled down in the second heating region can be further cooled to a temperature (T5), wherein the water cooled down in the first heating region can be supplied as cooling medium.
 12. Device according to claim 8, wherein the device comprises a water cycle in which the cooling region is connected to the first heating region, such that heated water from the cooling region can be supplied to the first heating region as heating medium for pre-heating the product, and the cooled water of the first heating region can be supplied to the cooling region as cooling medium.
 13. Device according to claim 8, wherein the device further comprises a product bypass conduit by which the product can be passed by the first heating region and directly to the second heating region.
 14. Method according to claim 6, wherein the viscosity of the product to be heated is within a range of 5 to 100 mPa·s.
 15. Device according to claim 9, wherein a heat exchanger section comprises at least one tubular heat exchanger or plate heat exchanger section. 